The broadcast of television and multimedia signals using satellite links has expanded steadily in recent years. Satellite television providers can offer a large number of high quality channels without requiring additional terrestrial infrastructure. Providing reliability in a satellite broadcasting system is therefore an important goal of satellite broadcast providers.
Historically used frequency bands (L, S, C, or Ku bands) for satellite services have gradually become congested, leading to the use of higher frequency bands such as the Ka-band (20-30 GHz). The Ku- and Ka-bands are now used for a significant portion of multimedia communications. The Ka-band provides a larger bandwidth than is available at lower frequencies, and most satellite communications providers are moving toward utilization of that frequency band.
Ka-band, however, is more susceptible to rain and atmospheric attenuation than are the lower frequency bands, because the resonant frequency of molecular water vapor absorption is located within the band, at 22.3 GHz. The resulting signal fading causes random bit errors and also causes the transmission operation to be completely lost for short periods of time. The signal attenuation usually occurs in small geographic areas (2-8 km in diameter) relative to the footprint of the transmission-beam, which may be approximately 650 km in diameter. Reception quality and channel conditions may therefore vary from subscriber station to subscriber station.
In response to demand for additional bandwidth, commercial satellite system designers are considering even higher frequency bands, including the V-band (40-75 GHz), which is currently being used for military applications. While providing greatly increased bandwidth, those higher frequencies suffer from more severe multi-path fading and scattering of transmitted signals.
Customers of satellite television services may therefore experience brief service outages due to adverse weather conditions. The term “rain fade” is commonly used to describe the attenuated signal and noticeable degradation of image quality. That degradation can be caused by rain, snow, ice, etc. In some cases, the signal is fully disrupted and the customer experiences a total loss of the viewing channel. Customers must wait until the weather clears and the signal is returned to normal. That can be very discouraging to customers who may be enjoying a favorite television program or sporting event only to have the broadcast interrupted by a loss of signal.
There is therefore a need to improve the reliability and quality of service of satellite broadcasting services.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.